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In spite of its frustrated lattice, the multiferroic
Lu0.5Sc0.5FeO3 exhibits two consecutive
magnetic transitions at TN1 ≈ 175 K and TN2 ≈ 70 K determined from neutron diffraction. In the ordered
state, magnetic fluctuations are present, most likely arising from the in-plane
frustrated interaction of the Fe hexagonal lattice. Furthermore, a crossover of
the magnetic intensity is observed from elastic to inelastic upon warming,
indicating that magnetic fluctuations persist well above TN1, a common feature in hexagonal multiferroics.

The multiferroic material Bi1-xSmxFeO3 shows ferroelectric and antiferromagnetic properties in
the ground state of the Bi-rich side. When the Sm content increases from
x = 0 in BiFeO3, the (ferroelectric-R3c
→ paraelectric-Pnma) state change occurs around x
= 0.14. According to the previous studies on
Bi1-xSmxFeO3, the state boundary between the R3c and Pnma states can be
identified as a morphotropic phase boundary (MPB), which is nearly parallel to
the temperature axis in the state diagram. The notable feature of
Bi1-xSmxFeO3 is that a remarkable piezoelectric response was also found
near the MPB. However, the origin of the remarkable response has not been
understood sufficiently. In this study, thus, the crystallographic features in
the vicinity of the MPB have been examined by x-ray powder diffraction and
transmission electron microscopy. It was confirmed that the R3c and Pnma states
were present for 0 ≤ x ≤ 0.15 and for
0.16 ≤ x ≤ 0.30, respectively. In
addition to these states, there also existed the PbZrO3-type state
around x = 0.15, which was identified as a modulated
structure. Based on the analysis of the modulated structure, furthermore, it was
suggested that the PbZrO3-type state could be regarded as a 2q state,
which is characterized by two transverse modulation waves with k1
= [1/2 0 0]o and k2 = [0 1/2
0]o in the orthorhombic-Pnma notation.

In the highly-correlated electronic system Ca1-xPrxMnO3 having the simple perovskite structure, it has been
reported that there exists the C-type orbital-ordered (COO) state accompanying
an antiferromagnetic ordering for 0.10 ≤ x
≤ 0.25. According to the previous studies concerning orbital-ordered
states in simple perovskite manganites, the COO state was understood to be
characterized by a spatial array of (3z2-r2)-type orbitals
for 3d electrons in Mn ions. The notable feature of the COO state in
Ca1-xPrxMnO3 is that the state with the monoclinic-P21/m
symmetry appears as a result of the structural transition from the disordered
state with the orthorhombic-Pnma symmetry. Compared with the COO-state formation
from the cubic-Pm
$\overline 3$
m state, however, the formation from the disordered-Pnma state
has not been understood yet. We have thus examined the crystallographic features
of the formation of the COO state in Ca1-xPrxMnO3, mainly by x-ray powder diffraction and transmission
electron microscopy. In the case of x = 0.16, for
instance, the COO state was found to appear from the disordered-Pnma state
around 90 K on cooling. The notable feature of the formation is that, in the
Pnma state just before the COO-state formation, characteristic diffuse
scattering appeared around each reflection in electron diffraction patterns,
together with the splitting of the 200c reflection in x-ray powder diffraction
profiles in the pseudo-cubic notation. Based on these experimental data, it is
understood that the formation of the COO state in Ca1-xPrxMnO3 accompanies remarkable fluctuations of the C-type orbital
ordering in the disordered-Pnma state.

Phase pure Pb[(Fe0.5-xScx)Nb0.5]O3 [x
= 0 to 0.5] multiferroic relaxors have been synthesized to study the
effect of Sc on dielectric phase tansition. Rietveld refinement of x-ray
diffraction patterns confirm that the structure transforms from monoclinic (Cm)
to rhomobohedral (R3m) at x = 0.3. Absence of low frequency dielectric
response in compositions with low Sc content attributed to interfacial
polarizabilty arising due to differences in conductivities of grain and grain
boundary. Moreover, value of diffusivity parameter (γ) of high of Sc
content compositions is near to 2, confirms relaxor charactertistic of these
compositions. However, an essential feature of relaxors i.e., frequency
dependent dielectric permittivity as a function of temperature is observed only
in x = 0.5 composition
[Pb(Sc0.5Nb0.5)O3 (PSN)]. In addition,
ferroelectric phase transition temperature (Tmax) increases initially
at lower Sc content (upto x ≤ 0.25), and further drops beyond x
≥ 0.3. Such behavior of Tmax in these compositions is due to the
onset of B'-B" local cation ordering at x = 0.3. High
temperature Raman spectra of Pb(Sc0.5Nb0.5)O3
(x = 0.5) confirm the stability of cation ordering in compositions with
high Sc content well above the phase transition temperature.

The multiferroic material YbMnO3 has been reported to exhibit both
ferroelectric and antiferromagnetic orders in the ground state. Of these two
orders, the ferroelectric order is associated with the
P63/mmc-to-P63cm structural transition, which occurs
around 1270 K. The interesting feature of the ferroelectric state is that a
cloverleaf domain structure with a pseudo-six-fold symmetry is observed in
transmission electron microscopy images with the beam incidence parallel to the
hexagonal axis. To understand the origin of the formation of the cloverleaf
domain structure, we have examined the crystallographic features of the
ferroelectric state in YbMnO3 by transmission electron microscopy. In
this study, particularly, we adopted the experimental condition that electron
beam incidences are perpendicular to the hexagonal axis. It was, as a result,
found that there existed various ferroelectric domain structures including the
cloverleaf domain structure under the present condition. The notable feature of
domain structures found in this study is that each domain structure basically
consists of six domains, whose domain boundaries are terminated at one point.
Because this feature makes us reminiscent of a discommensurate structure in an
incommensurate state, we took high-resolution electron micrographs of areas
including domain boundaries. Their analysis indicated that a domain boundary
could be identified as a discommensuration with a phase slip of π/3.
It is thus understood that the cloverleaf domain structure should be one of
domain morphologies for a discommensurate structure, which is related to the
break of the translational symmetry.

Transition metal oxide thin film heterostructures have garnered increasing
research interest in the last decade due to their multifunctional properties,
such as ferromagnetism and ferroelectricity, which may be utilized in next
generation device applications. Many previous works reported on the deposition
of such structures on oxide substrates such as SrTiO3, which are not
compatible with CMOS applications where Si(100) is the mainstay substrate
material. BiFeO3 (BFO) is a room temperature insulating ferroelectric
and antiferromagnet, a well-known multiferroic material. SrRuO3 (SRO)
is a ferromagnetic metal with the Curie temperature (TC) of 165K.
Unexpected properties emerge when these two dissimilar materials are conjoined.
However, there has been no report on exploring the magnetic properties of BFO
when it is in contact with SRO, and particularly when they are integrated with
Si(100) substrates, which is the subject of present study. BFO/SRO thin films
have been epitaxially grown on Si (100) substrates by introducing MgO/TiN
epitaxial buffer layers using pulsed laser deposition. BFO thin films show room
temperature ferroelectricity as observed from piezo force microscopy (PFM)
measurements. The magnetic data collected from BFO thin films show typical
antiferromagnetic features as expected. The TC of SRO in all the
samples studied was found be ∼ 170K, close to the reported value of
165K. Interestingly, we have noticed that the coercive field of SRO layer
increased from 4 kOe to 15 kOe (nearly fourfold) by reducing its thickness from
180 to 23nm, while keeping the thickness of BFO layer constant at 100nm. Pinning
of Ru ions by ferroelectric domain walls in BFO, strong interfacial exchange
coupling and SRO layer thickness could cause the observed enhancement in
coercivity. Our near future work will address the precise underlying mechanisms
in greater detail.

The presence of the C- and A-type orbital-ordered states has been reported in the
highly-correlated electronic system
Sr1-xNdxMnO3 (SNMO). The interesting feature of
the oxide system is that an increase in the Nd content leads to the (C-type
→ A-type) state change across a temperature-independent morphotropic
phase boundary (MPB). Although structural fluctuations can be expected near the
MPB, the detailed features of the state change have not been understood
sufficiently. Thus, the crystallographic features of the state change in SNMO
with 0.35 ≤ x ≤ 0.49 have been investigated mainly at 300
K, by x-ray powder diffraction and transmission electron microscopy. It was
found that the C-type orbital-ordered state with the tetragonal-I4/mcm symmetry
and the disordered orthorhombic-Imma state were present for 0.35 ≤ x
≤ 0.43 and for 0.45 ≤ x ≤ 0.49 at 300 K,
respectively. The notable feature of the state change is that disordered regions
with the cubic-Pm
$\bar 3$
m symmetry were also found locally for x
= 0.43, in addition to the C-type state. Because the
rotational-displacement pattern for oxygen octahedra involved in the
disordered-Imma state is the same as that in the A-type state, furthermore, the
former disordered state may be regarded as a precursor state to the A-type
orbital ordering.

YCrO3 (YCO) is known to be a multiferroic with orthorhombic,
Pnma, structure with center of inversion. However, the
local structural inhomogeneity in this compound is believed to give rise to
ferroelectric behavior. In this study we explore high temperature Raman
investigations of YCO and observed that one of its Raman mode B3g (3)
(CrO6 Octahedral tilt mode) softens around the structural phase
transition which could be the origin of ferroelectric nature in YCO. In
addition, we substitute bismuth (Bi) in YCO to understand the structural
distortions that lead to local structural inhomogeneity. Besides B3g
(3) mode softening with composition and high temperature studies in
Y1-xBixCrO3 the study reveals the
structural distortions and the structural tunability Bi offers in such
systems.

The simple perovskite manganite Sr1-xSmxMnO3 (SSMO) has been reported to have a highly-correlated
electronic system for eg-electrons in a Mn ion. According to the previous studies, the C-type
orbital-ordered (COO) state with the I4/mcm symmetry was found to be formed from
the disordered-cubic (DC) state on cooling. The feature of the COO state is that
its crystal structure involves both the Jahn-Teller distortion to orbital
ordering and the R25-type rotational displacement of oxygen octahedra. Because of the
involvement of both the distortion and the displacement, their competition
should be expected in the formation of the COO state. However, the detailed
features of the competition have not been understood yet. Thus, the
crystallographic features of the COO state in SSMO have been examined by x-ray
powder diffraction and transmission electron microscopy. It was found that, when
the Sm content increased from x = 0 at room
temperature, the DC state changed into the COO state with the tetragonal
symmetry around x = 0.13. The notable feature of the
COO state is that the state is characterized by a nanometer-scaled banded
structure consisting of an alternating array of two tetragonal bands. One
tetragonal band consisted of the COO state involving both the Jahn-Teller
distortion and the R25-type rotational displacement. But, there was only the latter displacement
in the other, the state of which could be identified as a disordered tetragonal
(DT) state. Based on this, it is understood that the COO-state formation from
the DC state should take place via the appearance of the DT state, which may
involve fluctuations of the C-type orbital ordering.